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A Realistic Breathing Phantom of the Thorax for Testing New Motion Mitigation Techniques with Scanning Proton Therapy

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R Perrin

R Perrin1*, M Peroni1 , K Bernatowicz1 , M Zakova1 , A Knopf1 , S Safai1 , T Parkel2 , A Lomax1 , (1) Paul Scherrer Institut, Psi-villigen, Aargau, (2) CSEM, Swiss Centre of Electronics and Microtechnology, Landquart, Graubunden


SU-D-BRE-1 Sunday 2:05PM - 3:00PM Room: Ballroom E

A prototype breathing phantom (named LuCa) has been developed which simulates the anatomy and motion of a patient thorax.In this work, we describe the results of the first commissioning tests with LuCa.

The phantom provides a close representation of the human thorax. The lungs,contained within a tissue-equivalent ribcage and skin,are made from a polymer foam,which is inflated and deflated using a custom-made ventilator. A tumor is simulated using a wooden ball with cutplanes for placing GafChromic films. The ventilator,controlled with Labview software,simulates a full range of breathing motion types.
Commissioning tests were performed to assess its performance using imaging (CT and radiographic) and film dosimetry as follows:i)maximum Tumor excursion at acceptable pressure ranges, ii)tumor Motion repeatability between breathing periods,iii)reproducibility between measurement days,iv)tumor-to-surface motion correlation and v)reproducibility of film positioning in phantom.

The phantom can generate repeatable motion patterns with sin⁴,sin,breath-hold (tumor amplitude repeatability <0.5mm over 10min),aswell as patient-specific motion types. Maximum excursions of the tumor are 20mm and 14mm for the large and small tumor inserts respectively. Amplitude reproducibility (Coefficient of Variation) averaged at 16% for the workable pressure range over 2 months. Good correlation between tumor and surface motion was found with R²=0.92. Reproducibility of film positioning within the thorax was within 0.9mm, and maximum 3° error from the coronal plane. Film measurements revealed that the film repositioning error yields relative errors in the mean dose over the planned target volume (PTV) of up to 2.5% and 4.5% for films at the center and on the edge of the PTV respectively.

Commissioning tests have shown that the LuCa phantom can produce tumor motion with excellent repeatability. However,a poorer performance in reproducibility of tumor amplitude for a given peak pressure week-to-week. Film set-up reproducibility is adequate for detection of dosimetric errors resulting from motion of >3%.

Funding Support, Disclosures, and Conflict of Interest: This work is funded by Swiss National Fund Grants 320030_127569 and 320030_1493942-1

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